This invention relates to managing a printer's consumables. More particularly, the invention is directed to estimating environmental conditions in order to more accurately predict when a printer will run out of a consumable such as toner.
It is generally known that electrophotographic printers utilize toner to generate text and/or images on a print medium, such as, paper. In this regard, a toner cartridge is typically employed to store a fixed amount of toner. When toner runs out in the middle of a print job, paper and time may be wasted, and users may become frustrated. Thus, when there is insufficient toner to complete a print job, it is desirable to provide a means for warning a user before printing is started. To assist in this goal, sensors are often utilized to measure the toner level in a cartridge. However, sensors are expensive, so methods for estimating toner usage are also employed.
Previous inventions have disclosed methods of estimating toner usage for a print job. Typically, the toner usage is estimated for each print job. If the estimate indicates that insufficient toner is remaining in the cartridge, a user may be notified. For example, U.S. Pat. No. 5,802,420 discloses a method of predicting toner usage based upon printing history. If a certain amount of toner was used to print the last 10 pages, the next 10 pages is estimated to use that same amount. U.S. Pat. No. 5,937,255 discloses a method of estimating toner usage based upon a pixel count. For example, if “T” amount of toner is used to generate one pixel, then 100 pixels is estimated to use 100×T amount of toner.
However, different pixels may not require the same amount of toner. An electrophotographic printer scans a light beam across the surface of an optical photoreceptor (“OPR”). To create a pixel, the light beam is modulated (or pulsed) to illuminate a desired pixel location. However, the pixel does not represent a fixed quantity of toner. For each pulse, the length of time (or duration) the light source is on as it scans across the OPR correlates to the width of the pulse on the OPR surface. The width and number of pulses used to create a pixel may vary from one pixel to another. For example, to produce certain fine details, it may be advantageous to produce relatively narrow pixels. Thus, the duration of the pulse used to create the relatively narrow pixel is be correspondingly short. Conversely, a pulses of a relatively longer durations are used to produce a substantially solid line.
Even for a given sized pixel, the amount of toner used may vary from pixel to pixel. For example, the number of pulses used to create a pixel may differ from pixel to another. A first pixel may be produced with a single pulse. A second pixel may be produced with more than one pulse. However, the first and second pixels may be substantially the same size despite using varying amount of toner based on the number and duration of each pulse.
The durations of the pulses required to produce pixels can be summed into a running pulse width count (RPWC). The RPWC is a measure of the accumulated duration of pulses over a given time period and can be used to more accurately estimate toner usage. In a controlled environment, a pulse of a set duration—one millisecond for example—requires a known amount of toner. Using this information and the capacity of a toner cartridge, the RPWC value required to deplete all toner in the cartridge can be determined. For example, a printer may require 0.0001 grams of toner for a pulse width of one millisecond. Where the same printer uses a cartridge that stores 100 grams of toner, the RPWC should obtain a value of 1,000,000 seconds by the time the toner is depleted. In other words, the expected pulse width count (EPWC) for the toner cartridges is 1,000,000.
By setting the RPWC to zero when a new cartridge is installed, the amount of toner remaining in the cartridge can be estimated. Using the example above, when the RPWC reaches 500,000, half of the toner should be gone. However, estimation of the rate of toner usage for a given RPWC value presumes a controlled environment with a set ambient temperature and set relative humidity. Variations in either the temperature or humidity cause more or less toner to be consumed for the same RPWC value. To improve printer quality, variations in environmental conditions should be taken into account when estimating toner usage.